Two methods of making “structured” drawn glass, having microchannels or nanochannels in the direction of the draw are commonly known and used. The first method is to start with a preform that contains two kinds of glass. A core glass is easily etched in acid, while a cladding glass is not etchable. The preform is drawn into fiber, cut perpendicularly to the drawing direction into segments, and the segments are bundled together in parallel. The drawing and bundling process can be repeated many times. Finally, the last bundle is fused, sliced perpendicularly to the drawing direction into segments of a desired thickness, and the core glass is etched out from both sides leaving an array of holes. The difficulty is that in cases where a segment is more than a few millimeters thick, the etching process can take a prohibitively long time, since the core glass is etched out through increasingly long, narrow channels. The article produced is known as microchannel or nanochannel glass.
The second method is used to make structured optical fiber (also known as photonic crystal fiber or holey fiber). In this case, the preform has holes (macro-channels) through it which can be produced by bundling solid and hollow rods or by bundling two kinds of glass, fusing and etching out one glass before drawing (Falkenstein, et al, Optics Letters vol. 29, p. 1858, 2004). In either case, the preform has holes through it when it is ready for drawing. The preform is then drawn once or repeatedly to make the fiber. The difficulty is that the holes tend to collapse and/or distort during the final fusing process.